Chemotherapy using cytotoxic drugs is presently the most commonly used weapon in the treatment of advanced cancer. However, the therapeutic efficacy of cancer chemotherapeutic agents is limited by factors such as tumor heterogeneity, host toxicity and drug resistance. Recent advances in drug development have provided new opportunities to improve cancer therapy using drugs that target the tumor vasculature and inhibit tumor angiogenesis. To date, however, the survival benefit of these angiogenesis inhibitors has been rather modest and efforts to improve activity by combination with conventional chemotherapeutic drugs have been only partially successful. The overall goal of this project is to develop novel, more effective approaches to combining angiogenesis inhibitors with traditional cancer chemotherapeutics, building on progress made in the last project period in studies using the VEGF receptor-selective tyrosine kinase inhibitor axitinib and the liver cytochrome P450-activated anti-cancer prodrug cyclophosphamide. The major aims of this proposal are: 1) to elucidate the mechanism whereby anti-angiogenic drug treatment blocks tumor regression induced by metronomic cyclophosphamide treatment and then devise alternative therapeutic approaches that circumvent this block; 2) to investigate the use of provascular strategies to enhance tumor delivery of cancer chemotherapeutic drugs given in conjunction with anti-angiogenesis; 3) to harness the anti-vascular effects of anti-angiogenic drugs so as to increase tumor cell exposure to cytotoxic drugs administered intratumorally via an intratumoral 'trapping' (enhanced drug retention) mechanism; and 4) to investigate the impact of changes in tumor microvessel density, neovascularization and vascular maturity on responsiveness to the combination of anti-angiogenic drug treatment with chemotherapy. Together, these studies will elucidate ways to increase responsiveness to anti-angiogenic drugs by combination with conventional chemotherapeutic agents in a way that improves overall therapeutic activity, and will thereby advance the development of anti-cancer therapies.